1. Field of the Invention
The present invention relates to a safety means for a heating apparatus for use with electric appliances such as an electric oven or an electronic range each having a digital control portion or for compound ovens and so on, and for use with apparatus such as washing machines or coolers. The safety means detects the errors of the input power-supply voltage, the failures of the respective heating means and control means, and displays the detected failure and safely stop the associated electric appliances.
In terms of heating apparatuses, single function electronic ranges, single function electric ovens, commodities intended for higher outputs by two high-frequency generating apparatuses mounted therein, compound devices having both the heater heating and high-frequency heating to realize alternate or simultaneous heating have been offered for sale, a high-frequency heating apparatus with two high-frequency heating apparatuses being mounted therein requires a high-tension transformer, a high-tension capacitor, a magnetron and a high-tension diode, and a relay apparatus, such as a relay and so on for controlling them. The frequency of failures of the functional components increases with the increase in the number of components. The failures of the functional components may cause an abnormal current flow which may cause an extremely danger condition.
Also, more time is needed to locate which component is out of order so as to repair it, because the number of components has increased.
Many input voltages are provided because of internationalization of the devices. For example, since both 208 V and 230 V may be disposed in the same outlet style in North America, the incorrect connection of the apparatuses may often be made. For example, when the tap of the primary side of the low-tension transformer and the high-tension transformer of the high-frequency heating apparatus having a digital control portion, which is set in 208 V, is connected to a power supply of 230 V, the voltage which is higher by approximately 10% (230 V/208 V.apprxeq.1.1) than normal is outputted onto the secondary side, with the inconvenience that the service life of the apparatuses such as the magnetron of a high-frequency generating apparatus becomes considerably shorter. When the tap on the primary side of the apparatus is set at 230 V, the high-frequency output becomes smaller than normal when the power-supply of 208 V is connected with the inconvenience that the cooking time becomes longer.
In the heater heating operation of a sheathed heater and so on, the heating output varies by approximately 20% with change in the 10% input voltage, with the inconveniences that the heating becomes excessive (PO=V.sub.IN 2/R) or the temperature does not reach its set value. These incorrect connections are often found for the first time when the cooking performance has been inferior after long usage, because the incorrect connections are hard to detect.